1. Field of the Invention
This invention relates to a forward and reverse rotation mechanism for forward and reverse movement used in an original reading apparatus or the like, and in particular to such a mechanism for effecting rotation in one direction as a drive source.
2. Related Background Art
Forward and reverse rotation mechanisms for effecting forward and reverse movement of a rotatable member, a reciprocally movable member or the like, have heretofore been of the type which uses a motor effecting forward and reverse revolution as a drive motor, or of the type in which rotational force from a drive motor revolving in one direction is forwarded or reversed by the use of two electromagnetic clutches and by controlling these electromagnetic clutches.
However, the former has the disadvantage that the motor effecting forward and reverse rotation is expensive and difficult to control, and the latter has the disadvantage that although the motor revolves in one direction, the electromagnetic clutches are expensive and bulky.
In view of such problems, a mechanism which does not use a forwardly and reversely revolvable motor and magnetic clutches but utilizes two spring clutches to forward or reverse the one-way rotational force from the drive source revolving in one direction, is considered in U.S. Pat. No. 4,458,796.
Spring clutches are small and inexpensive as compared with electromagnetic clutches, and preferably enable the forward and reverse rotation mechanism utilizing them to be compact and low in cost.
However, in the construction described in the aforementioned U.S. Pat. No. 4,458,796, the connection between the motor and the original carriage is released only when the original carriage has been returned to its home position during the scanning of an original. That is, the connection between the motor and the original carriage cannot be released when the original carriage has been stopped outside its home position due to jam or erroneous opening of the main switch, and this leads to the problem that the original carriage is not freely moved.
Also, to stop movement of the original carriage outside its home position, revolution of the motor must be stopped. In this state, the connection between the motor and the original carriage is not cut off, and the inertia of the original carriage may adversely affect the forward and reverse rotation mechanism.